Time delay relay

ABSTRACT

A time delay relay comprising a set of electrical contacts movable between circuit-making and circuit-breaking positions and thermally responsive means for actuating the contacts to move them from one to the other position at a predetermined temperature. The relay includes thermal storage means in heat exchange relationship with the thermally responsive actuating means. The thermal storage means comprises a body of material which will change from a first to a second physical state at a temperature intermediate that of the ambient of the relay and the predetermined temperature. Heatable means is positioned in heat exchange relationship with the thermal storage means so as to effect a transfer of heat therebetween and cause the body of material to change states so that the transfer of heat between the heatable means and the thermally responsive means is delayed and the period of time required for the thermally responsive means to reach the predetermined temperature is extended.

United States Patent [191 [11] 3,845,440

Hunter Oct. 29, 1974 i 1 TIME DELAY RELAY [75] Inventor: Eugene A.Hunter, Plano, Tex. ABSTRACT ['73] Assignee; Texas InstrumentsIncorporated A time delay relay comprising a set Of electrical Dallas,Tex. contacts movable between circuit-making and circuitbreakingpositions and thermally responsive means for [22] Wed: 1973 actuatingthe contacts to move them from one to the 2 APPL 421,552 other positionat a predetermined temperature. The relay includes thermal storage meansin heat exchange relationship with the thermally responsive actuating[52] US. Cl 337/341, 337/3, 337/298, means The thermal Storage meanscomprises a body 1337/1101 of material which will change from a first toa second Ft. Cl. p y l state at a temperature intermediate h of [58]held of Search 337/401 30 the ambient of the relay and the predeterminedtem- 337/336' 60/528 529 perature. Heatable means is positioned in heatexchange relationship with the thermal storage means so [56] Referencescued as to effect a transfer of heat therebetween and cause UNITEDSTATES PATENTS the body of material to change states so that the trans-3,575,645 4/1971 Doversberger et al. 337/3 fer of heat between theheatable means and the ther- 3,624,578 11/197! Stocker et a1 337/299mally responsive means is delayed and the period of PrimaryExaminer-Har0ld Broome Attorney, Agent, or FirmJohn A. Haug; James P.McAndrews; Edward J. Connors, Jr.

time required for the thermally responsive means to reach thepredetermined temperature is extended.

10 Claims, 2 Drawing Figures TIME DELAY RELAY BACKGROUND OF THEINVENTION This invention relates to time delay relays and moreparticularly to thermal time delay relays.

As the use of such relays in many types of control systems hasincreased, there has been a growing need for thermal time delay relayswhich would provide longer time delays. In order to increase the delayperiods of these relays the thermal mass thereof has been increasedand/or the operating temperature has been elevated. However, it isimpractical to increase the size and operating temperatures sufficientlyto achieve extended time delays of, for example, several hours,particularly where the available mounting space and applicationrequirements limit such increases in size and operating temperature.

SUMMARY OF THE INVENTION Among the several objects of this invention maybe noted the provision of time delay relays which have extended periodsof delay and yet are compact in size and do not require excessiveoperating temperatures and the provision of such thermal time delayrelays which are economical in construction and reliable in operation.Other objects and features will be in part apparent and in part pointedout hereinafter.

Briefly, a time delay relay of this invention comprises a set ofelectrical contacts movable between circuitmaking and circuit-breakingpositions and thermally responsive means for actuating said contacts tomove them from one position to the other at a predetermined temperature.Thermal storage means are positioned in heat exchange relationship withthe actuating means. The storage means is constituted by a body ofmaterial which will change from a first to a second physical state at atemperature intermediate that of the ambient of the relay and thepredetermined temperature. A heatable means, such as an electricalresistance heater, is positioned in heat exchange relationship with thethermal storage means so as to effect a transfer of heat therebetweenand cause the body of material to change states so that the transfer ofheat between the heatable means and the thermally responsive means isdelayed and the period of time required for the thermally responsivemeans to reach the predetermined temperature is extended.

BRIEF DESCRIPTION OF DRAWINGS DESCRIPTION OF A PREFERRED EMBODIMENTReferring now to the drawings, a thermal time delay relay of thisinvention is indicated generally at reference numeral 1. This relaycomprises a thermostatic switch 3 including a thermally responsiveactuator 5, a thermal storage device 7' and a heater 9 stacked within acompartment 1:1 of an insulated housing 13. These components are held inrespective contact with each other within the insulated compartment byan insulating cover 15 that has depending retainer lugs 15a to maintainthe switch and storage device in coaxial alignment, and a springterminal finger 17 that biases the entire stacked assembly against theinner surface of the cover.

Switch 3 has a switch arm 19, one end of which is welded to the innerend of a terminal lug 21. The free end of switch arm 19 has a pair ofopposed contacts 23 movable between two fixed or stationary contacts25,27 constituted by the inner ends of terminal lugs 29,31. These threelugs are secured in an inverted cupshaped case 33 of insulatingmaterial.

The intermediate portion of switch arm 19 is dimpled to provide a boss35 aligned with one end of a transfer pin 37 axially slidable in a bore39 of a generally cylindrical pin guide 41. The other end of pin 37rests on the central portion of thermal actuator 5 constituted by asnap-acting composite bimetallic disc, such as disclosed in US. Pat. No.1,448,240. Because of the nondevelopable or dished shape of thethermally responsive disc 5, it will snap from one curavture position toan opposite curvature position upon the temperature increasing to apredetermined level and will abruptly reverse its curvature when cooledbelow that level.

The undersurface of guide 41 is recessed to accommodate the flexingmovement of disc 5 which peripherally rests on an annular ledge formedby a cup-shaped closure 43, the upper end of which is swaged over andgrips the lower edge of housing 33 to secure together the housing andpin guide. Closure 43 is formed of a thermally conductive material, suchas aluminum or copper, to provide excellent heat transfer with and heatexchange between thermal storage device 7.

Thermal storage device 7 comprises a capsule or cartridge of a thermallyand electrically conductive material, such as aluminum or copper,partially filled with a body of material 45 which will change from onephysical state to another at a temperature between ambient and thetemperature at which the disc will snap to actuate the contacts. Thebody of material 45 contained in capsule 7 may be either a solid or aliquid at ambient temperatures of the relay. If a solid material isused, its fusion temperature is somewhat below that at which the discsnaps. If material 45 is a liquid at ambient temperatures, it willvaporize or boil at a temperature somewhat less than the actuationtemperature of the switch. Exemplary of thermal storage materials thatare solid at ambient temperatures but change to a liquid state or fuseat temperatures within typical operating ranges of thermal relays aremany different waxes and paraffms, Roses and Woods metals and sulfur.These materials have melting pointsthat range between about and 250F.Glycerol which melts at about 68F. but solidifies at lower temperaturesis another useful thermal storage material. These materials have heatsof fusion ranging from about 12-100 Btu/lb. Typical thermal storagematerials that are liquid at ambient relay temperatures but boil attemperatures below maximum useful operating temperatures of thermalrelays are methanol, ethanol and water with boiling points between aboutl50F. and 212F. and heats of vaporization between about 365-950 Btu/lb.

Heater 9 is a pill or disc of an electrical resistance material,preferably one formed from a steepsloped positive temperaturecoefficient (PTC) material such as certain doped barium titanates. It issecured to the undersurface of thermal capsule 7 and supplied withelectrical power by means of terminal finger 17 ofa terminal'lug 47which extends outwardly through cover and another terminal lug 49 theinner end of which has a similar spring finger 51 contacting theelectrically and thermally conductive capsule 7.

Operation of relay 1 is as follows: Assuming that at ambient relaytemperatures the switch contacts and disc 5 are in the solid linepositions and electrical power is supplied toheater 9 via terminalfingers 17 and 51, the heater will generate heat with its resistanceincreasing with temperature until it reaches stabilization current andtemperature conditions at a level that exceeds that at which disc 5 willsnap into its broken line position and move contact arm 19 into itsbroken line position. However, as the thermal storage material is heatedto the temperature at which it will change state, heat will continue tobe absorbed by the heat storage device and contained thermal storagematerial without any substantial change in the temperature thereof untila sufficient quantity of heat is absorbed to effect a change of state ofthe material. This heat of fusion or vaporization may be many times thenormal heat capacity of the material and thus the heat content of thematerial 45 is greatly increased as it undergoes a change in statewithout any substantial change in temperature. Therefore the thermalstorage device or thermal capacitor 7 delays the transfer of heatbetween the heater 9 and the thermal actuator disc 5 until sufficientheat is absorbed by material 45 and thereafter it will increase intemperature with further heat input until the operating temperature ofdisc 5 is reached.

As switch 3 may be connected into any conventional control circuit as anormally open or normally closed switch, the abrupt lifting of pin 37 asdisc 5 snaps will open or close the circuit as desired. After this timedelay in actuation of relay 1, the switch contacts thereof will remainin the broken line positions as long as electrical power continues to besupplied via terminal lugs 47.49 and disc 5 will be maintained at atemperature determined by the stabilization current and temperature ofthe PTC heater 9.

A similar time delay is achieved as material 45 is permitted to cool toan ambient temperature or one below that at which material 45 changesstate to its original state and disc 5 abruptly returns to its solidline position and pin 37 moves down permitting the switch arm 19 toreturn to its solid line position. Thus relay 1 is effective as anextended time delay relay when permitted to cool from its operatingtemperature as well as being heated thereto. in both instances the heatabsorbed or given off as material 5 changes from one to the other of itsphysical states delays the change in temperature ofdisc 5 and theactuation of the set of switch contacts.

A typical application for thermal relays of this invention is as adefrost initiation thermostat in a refrigerator-freezenln such anapplication the ambient of the relay would be about 35-55F. or perhapslower, but in any event well below the temperature at which the thermalstorage material will change from a solid to a liquid, or a liquid to agas. The heater 9 stabilizes at a temperature of over l00F., forexample, and the thermal actuator is maintained in its hot" curvatureposition at this temperature. The time delay utilized would be thatrequired to permit the temperature of the disc and thermal storagedevice to drop to a temperature of about 50F. or less whereupon the discwill abruptly change its curvature from its hot to its cold position.FIG. 2 illustrates the extended time delay obtained with a relay 1 usinga thermal storage device with 97.1 g. of wax (obtainable under the tradedesignation DW37 from Dura Commodities Corporation of Harrison, NY.)with a melting point of about F, a specific heat of 0.465 Cal/g. 25C.and a heat of fusion of 55.3 Cal./g. The solid line curve of FIG. 2illustrates the relation of temperature to time of relay 1 after thepower to the heater 9 is cut off and the relay cools in an environmentof about 52F, the refrigerator ambient, as illustrated by the dashedline curve. As indicated, the relay temperature decreases in about 15minutes from about F. to about 80F. at which temperature the relaysubstantially remains for about 3 /2 hours during the transition orchange of state of the wax from a liquid to a solid, after which therelay temperature will drop to the refrigerator ambient of about 52F. inabout 45 minutes. Thus the delay between the time of deenergization ofheater 9 and the snapping of the disc as it actuates from its hot" toits cool" curvature is greatly extended by the heat given off, in thisinstance, during the change of state of the wax.

It will be understood that the extent of the delay is convenientlycontrolled by the type and amount of thermal storage material used, theshape and type of capsule or container utilized for device 7, the typeof heater used, the amount of insulation employed and the operatingtemperatures and differential of the thermal actuator used. Thus oneskilled in the art can conveniently provide relays with any preselecteddelay and operating range in accordance with the present invention.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. A time delay relay comprising:

a set of electrical contacts movable between circuitmaking andcircuit-breaking positions;

thermally responsive means for actuating said contacts to move them fromone to the other position at a predetermined temperature;

thermal storage means in heat exchange relationship with the thermallyresponsive actuating means, said storage means comprising a body ofmaterial which will change from a first to a second physical state at atemperature intermediate that of the ambient of the relay and thepredetermined temperature; and

heatable means in heat exchange relationship with said thermal storagemeans adapted to effect a transfer of heat therebetween and cause saidmaterial to change states whereby the transfer of heat between saidheatable means and the thermally responsive means is delayed and theperiod of time required for the thermally responsive means to reach thepredetermined temperature is extended.

5. A relay asset forth in claim 1 wherein the storage means material isa liquid at ambient temperatures and a gas at the predeterminedtemperature.

6. A relay as set forth in claim 4 wherein the storage means material isa wax.

7. A relay as set forth in claim 4 wherein the material is glycerol.

8. A relay as set forth in claim 3 wherein the thermally responsivemeans is a dish-shaped bimetallic disc which abruptly changes itscurvature as its temperature exceeds the predetermined temperature andwill abruptly revert to its original curvature after the temperaturethereof falls below the predetermined temperature. 1 9. A relay as setforth in claim 8 wherein the storage means material is one that is asolid at ambient temperatures and a liquid at the predeterminedtemperature.

10. A relay as set forth in claim 9 wherein the relay contacts,thermally responsive means and heater are all enclosed in a housing ofthermal insulation material.

1. A time delay relay comprising: a set of electrical contacts movablebetween circuitmaking and circuit-breaking positions; thermallyresponsive means for actuating said contacts to move them from one tothe other position at a predetermined temperature; thermal storage meansin heat exchange relationship with the thermally responsive actuatingmeans, said storage means comprising a body of material which willchange from a first to a second physical state at a temperatureintermediate that of the ambient of the relay and the predeterminedtemperature; and heatable means in heat exchange relationship with saidthermal storage means adapted to effect a transfer of heat therebetweenand cause said material to change states whereby the transfer of heatbetween said heatable means and the thermally responsive means isdelayed and the period of time required for the thermally responsivemeans to reach the predetermined temperature is extended.
 2. A relay asset forth in claim 1 wherein the heatable means is a heater forsupplying heat to the thermal storage means.
 3. A relay as set forth inclaim 2 wherein the heater is a body of electrical resistance materialhaving a positive temperature coefficient.
 4. A relay as set forth inclaim 1 wherein the storage means material is one that is a solid atambient temperatures and a liquid at the predetermined temperature.
 5. Arelay as set forth in claim 1 wherein the storage means material is aliquid at ambient temperatures and a gas at the predeterminedtemperature.
 6. A relay as set forth in claim 4 wherein the storagemeans material is a wax.
 7. A relay as set forth in claim 4 wherein thematerial is glycerol.
 8. A relay as set forth in claim 3 wherein thethermally responsive means is a dish-shaped bimetallic disc whichAbruptly changes its curvature as its temperature exceeds thepredetermined temperature and will abruptly revert to its originalcurvature after the temperature thereof falls below the predeterminedtemperature.
 9. A relay as set forth in claim 8 wherein the storagemeans material is one that is a solid at ambient temperatures and aliquid at the predetermined temperature.
 10. A relay as set forth inclaim 9 wherein the relay contacts, thermally responsive means andheater are all enclosed in a housing of thermal insulation material.